Polyurethane foams produced by the catalytic reaction of a polyisocyanate with a polyol in the presence of various blowing additives are widely known and used in fabricating parts and equipment for the automotive industry, as well as housing and other industries. One such blowing additive is a chlorofluorocarbon (CFC) blowing agent which vaporizes as a result of the reaction exotherm. The discovery that CFC""s may deplete ozone in the stratosphere has resulted in mandates diminishing CFC use. Production of water-blown foams, in which blowing is performed with CO2 generated by the reaction of water with the polyisocyanate, has therefore become increasingly important.
The production of rigid polyurethane foams is a well-known art, and as such, foams have a wide variety of industrial and commercial applications. Rigid polyurethane foams have been used as packaging materials, flotation materials and various structural components. Rigid polyurethane foam has one of the lowest thermal conductivity ratings of any insulant, which allows efficient retention of heat or, alternatively, maintenance of a refrigerated or frozen environment insulating rigid polyurethane foams may be molded into many useful appliances. The foams may be shaped into sheets of varying thickness and placed between roofs or in floors. They also may be formed into contour shapes useful in insulating pipes and ducts. Rigid polyurethane foam can also be applied to numerous substrates by spray foaming techniques. Spray foam applications are important particularly in such areas as warehouses, schools and offices providing the desired insulation requirements for heating and cooling.
Virtually all commercially manufactured polyurethane foams are made with the aid of at least one catalyst. Catalysts are those compounds that help promote the reaction between an isocyanate and an isocyanate-reactive compound. The types of catalysts that are typically utilized in the formation of rigid polyurethane foams may differ depending on application. The ability to selectively promote either the blowing reaction (reaction of water with isocyanate to generate CO2), the gelling reaction (reaction of polyol with isocyanate) or the trimer reaction (polymerization of isocyanate to form isocyanurate) is an important consideration in selecting the proper catalyst.
If a catalyst promotes the blowing reaction to a high degree, much of the CO2 will be evolved before sufficient reaction of isocyanate and polyol has occurred, and the CO2 will bubble out of the formulation, resulting in a foam of poor quality and physical properties. In contrast, if a catalyst too strongly promotes the gelling reaction, a substantial portion of the CO2 will be evolved after a significant degree of polymerization has occurred. This foam will typically be characterized by high density, broken or poorly defined cells, and/or other undesirable features. Finally, in those applications desiring the production of isocyanurate (trimer), if a catalyst does not generate enough heat (exothermic reaction) early on in the reaction, the amount of trimer that is produced will be low. Again, a poor quality foam, this time characterized by friability, poor dimensional stability and poor fire properties, will be produced.
The following patents and articles are representative of the art in the polyurethane industry:
U.S. Pat. No. 4,200,699 discloses the formation of rigid polyurethane foams using a catalytically effective amount of an antimony carboxylate, a potassium carboxylate, and a zinc carboxylate in combination with tertiary amines or tin compounds.
U.S. Pat. No. 5,342,859 discloses the use of alkali metal catalysts in the presence of excess carboxylic acid, e.g., 2-ethyl-hexoic acid to help improve the flame suppression of polyurethane foam by creating flame resistant amides. It also can help to reduce the water content of in polyurethane formation.
U.S. Pat. No. 6,107,355 discloses the use of alkali and alkaline earth metal salts of mono carboxylic acids to produce polyurethane foams. Cocatalysts consisting of tertiary amines may be used in conjunction with the metal salts.
U.S. Pat. No. 4,256,848 discloses the use of co-catalyst combinations comprised of divalent mono-mercuric salts of organic acids and ionizable mono-organo-mercuric carboxylates as catalysts for the preparation of polyurethanes including solid, non-cellular, and foam urethanes, both rigid and flexible.
U.S. Pat. No. 4,256,847 discloses a method for producing rigid polyurethane foams consisting of an organic polyisocyanate, an organic polyol, a blowing agent, and a catalyst. The catalyst suited for catalyzing the formation of polyurethanes consists of zinc or lithium salts of carboxylic acids.
U.S. Pat. No. 6,242,555 discloses the use of organo bismuth, organo fin and organo lead carboxylates as catalyst types for the production of micro-cellular or noncellular, light stable elastomeric isophorone diisocyanate based polyurethane moldings. Organobismuth carboxylates having less than 60% free acid, preferably less then 25% and most preferably, less than 10% are disclosed.
Arenivar, J. D., Bismuth Carboxylates for Polyurethane Catalysts., Polyurethanes, 89, Proceedings of the SPI 32nd Annual Technical/Marketing Conference, Oct. 1-4, 1989, pp 623-627 disclose the use of Bismuth Carboxylates for Polyurethane elastomers and the effect of added acid. Bismuth octoate and bismuth neodecanoate in the presence of 1-4 equivalents acid were disclosed as catalytic materials.
Although organometallic catalysts have found acceptance in many commercial coatings, adhesives, sealants, and elastomers (C.A.S.E.) applications, their use in urethane-based flexible and semi-flexible foams has been limited. Tertiary amines are currently the industry standard polyurethane foam catalyst, yet their distinct odor and volatility has had the industry searching for catalytic alternatives.
The present invention relates to an improvement in flexible, semi-flexible and rigid foams formed by the catalytic reaction of a reaction mixture comprised of an aromatic polyisocyanate, an organometallic catalyst, a polyol and a blowing agent. The improvement resides in a bismuth carboxylate or bismuth sulfonate having less than 34% free acid as the organometallic catalyst.
Several advantages can be achieved by the use of a bismuth carboxylate or bismuth sulfonate as the catalyst and these include:
an ability to produce flexible, semi-flexible and rigid foams of excellent quality;
an ability to produce a foam having an excellent low value of thermal conductivity;
an ability to produce a foam having essentially no odor; and,
an ability to reduce cell size and improve insulating properties (k-factor value).